Ladder leveling and stabilizing means

ABSTRACT

A ladder having leveling means is disclosed in which the leveling means functions to position and stabilize the ladder in an upright position on irregular, sloping, or unevenly firm terrain. The leveling means comprises a torsion bar that is rotatively journaled within a pair of brackets formed on the ladder side rails. The torsion bar is dimensional to extend across the bottom of the ladder. A pair of legs is perpendicularly mounted on the outer extremities of the torsion bar, the legs being oriented 180* from each other to extend in the opposite directions from the torsion bar. A shoe is rotatively attached to the outer end of each leg to be supported on the ground. The torsion bar and legs function to rotatively move in unison to enable the shoes to come to rest firmly on the ground, while maintaining the torsion bar in a level position and the ladder in an upright position. The torsion bar is then adapted to be locked in this rested position by a locking assembly. A typical locking assembly comprises a locking wheel or wheel sector fixedly connected to the torsion bar and a locking pawl pivotally connected to the ladder. The locking pawl is adapted to be manually movable to engage the teeth of the locking wheel or wheel sector to lock the torsion bar against rotation.

United States Patent [191 Luther 1 Apr. 23, 1974 LADDER LEVELING AND STABILIZING MEANS [76] Inventor: Philip Luther, 6861 Aura, Reseda,

Calif.91335 22 Filed: July 6,1973

21 Appl. No.: 377,141

Primary Examiner-Reinaldo P. Machado Attorney, Agent, or Firm-Robert M. Vargo, Esq.

[57] ABSTRACT A ladder having leveling means is disclosed in which the leveling means functions to position and stabilize the ladder in an upright position on irregular, sloping, or unevenly firm terrain. The leveling means comprises a torsion bar that is rotatively journaled within a pair of brackets formed on the ladder side rails. The torsion bar is dimensional to extend across the bottom of the ladder. A pair of legs is perpendicularly mounted on the outer extremities of the torsion bar, the legs being oriented 180 from each other to extend in the opposite directions from the torsion bar. A shoe is rotatively attached to the outer end of each leg to be supported on the ground. The torsion bar and legs function to rotatively move in unison to enable the shoes to come to rest firmly on the ground, while maintaining the torsion bar in a level position and the ladder in an upright position. The torsion bar is then adapted to be locked in this rested position by a locking assembly. A typical locking assembly comprises a locking wheel or wheel sector fixedly connected to the torsion bar and a locking pawl pivotally connected to the ladder. The locking pawl is adapted to be manually movable to engage the teeth of the locking wheel or wheel sector to lock the torsion bar against rotation.

18 Claims, 9 Drawing Figures ATEP-HEBAPRw W I 3,805,917 SHEET 1 [IF 4 PATEHTED APR 2 3 I974 SHEET l UF 4 LADDER LEVELING AND STABILIZING MEANS BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to portable ladders and more particularly to adjustable ladder supports which function to keep the ladders in substantially upright positions under any circumstances.

Portable ladders are of two general types: (1) nonself-supporting, such as the conventional runged ladder consisting of two side rails joined at regular intervals by crosspiece rungs, steps, or cleats, requiring a fixed structure against which the ladder can be leaned, and (2) self-supporting, such as the conventional stepladder.

The present invention is applicable to one or both pairs of side rails of self-supporting ladders, but its wider usage will be on the conventional non-selfsupporting ladder which, for safety, requires four-point support top and bottom of each side rail both before and after the ladder is loaded. The problem of bottom support due to uneven terrain, uneven firmness of the terrain, or a combination of both, is surmountable with the present invention.

2. Description of the Prior .Art

Conventional ladders have two very serious shortcomings.

One shortcoming occurs in utilizing a ladder on sloping or rough ground. Under these conditions, it is usually necessary to block up one leg of the ladder to position the ladder in a proper upright position. The problems encountered with such blocking procedures are: (1) they are time-consuming, (2) the ladder is usually unstable, and (3) the difference in the friction coefficients between the ground and the support block may be conducive to dislodgement of one leg of the ladder.

Another shortcoming occurs when supporting surfaces are unequal in supporting ability. When this happens, any application of a person s weight on the ladder could cause the ladder to sink. Under these conditions, substantially all of the weight of the person is supported on one leg of the ladder and only the friction of the upper end of the ladder against the wall holds the ladder upright. As a result, the ladder and the person on it is placed in a very precarious position in these situations.

Various ladders have been patented which attempt to alleviate the shortcomings of conventional ladders as described above.

One such ladder is described in U.S. Pat. No. 2,503,626. The patented ladder includes a pair of movable leg members slidably mounted on the bottom legs thereof. Each of the movable leg members is individually adjustable to extend beyond the respective leg of the ladder a distance necessary to keep the ladder in an upright position.

The major shortcoming with the ladder described in U.S. Pat. No. 2,503,626 is that the leg extensions do not function automatically. As a result, the setting up operation for such a ladder is quite cumbersome. Besides holding on to the ladder while it is being set up, the leg extensions and hand locks must be simultaneously manipulated. Such an operation would be quite difficult for one man to accomplish.

U.S. Pat. No. 2,835,427 also discloses a ladder having adjustable leg extensions for supporting the ladder in all types of sloping terrain. The leg extensions are interconnected by means of a pair of flexible straps of spring steel to enable the movement of one of the supports in one direction to cause the other support to move in the opposite direction.

The major shortcoming with the ladder described in U.S. Pat. No. 2,835,427 is that the structure is relatively complex and expensive. .This, of course, makes the production and marketing of the ladder economically unfeasible. Also, the premise that both friction locks will unlock instantaneously and simultaneously to allow the ladder to drop straight down while one side rail extension sinks through soft terrain, after which both friction locks must simultaneously relock; this free-fall feature, during which the ladder might slip sideways, or the locks not operate in unison, could introduze a hazard worse than exists without the leveling device.

U.S. Pat. No. 2,046,516 also discloses a ladder support for supporting a ladder on sloping terrain. However, the mechanism is so complex and cumbersome as to be totally impractical for present day use.

SUMMARY OF THE INVENTION The present invention obviates the above-mentioned shortcomings by providing a ladder having leveling means that is automatically adjustable to be set up 'on any irregular, sloping, or unevenly firm surface while still being simple and economical in construction.

The ladder leveling means comprises a torsion bar rotatively mounted adjacent the bottom ends of the ladder side rails. A pair of legs are mounted on the extremities of the torsion bar and are adapted to extend perpendicularly therefrom in opposite directions. A shoe is rotatively attached to the outer end of each of the legs to be supported on the ground. The torsion bar and legs are adapted to move freely as the ladder is being positioned on a sloping terrain to enable the oppositely extending legs to rotate until both shoes are firmly planted on the ground. Also, if the supporting surface is not equally firm under each shoe, the user may pre-load the ladder by standing or jumping on the bottom rung to sink the shoes until the supporting pres sure under each shoe is essentially equal and sufficient to carry the weight of the loaded ladder.'Being unlocked, the interconnecting torsion bar is free to rotate if the shoes sink to differing elevations. During this orientation, and after the torsion bar and legs have reached their adjusted angular position, the torsion bar is maintained in a horizontal position and the ladder is maintained in an upright position. The torsion bar is then locked in this adjusted position by a hand manipulated locking assembly. One type of locking assembly comprises a wheel fixedly connected to the torsion bar, and a locking pawl pivotally connected to the ladder. The locking pawl is adapted to engage the peripheral teeth of the wheel to lock the torsion bar against rotation.

The primary advantage of the present invention is that in achieving four-point support of the ladder, top and bottom of each side rail, the orientation of the legs function automatically and in unison while the ladder is set up on irregular, sloping, or unevenly firm terrain, thereby enabling the operation thereof easy and efficient.

Another advantage of the present invention is that the locked torsion bar functions to provide a stabilized,

' the torsion bar.

The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. The present invention, both as to its organization and manner of operation, together with further objects and advantages thereof, may best be understood by reference to the following description, taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a ladder having leveling means of the present invention;

FIG. 2 is an enlarged elevational view of the ladder leveling means;

FIG. 3 is an enlarged side elevational view of the ladder leveling means;

FIG. 4 is a schematic view of the ladder showing the operation of the leveling means;

FIG. 5 is a schematic view of the ladder showing the leveling means in a second operating position;

FIG. 6 is an enlarged side elevational view of a second embodiment of the ladder leveling means;

FIG. 7 is an enlarged side elevational view of a third embodiment of the ladder leveling means;

FIG. 8 is a fragmentary view of a shoe utilized'in the ladder leveling means; and

FIG. 9 is a schematic view of the ladder and torsion bar showing the legs oriented other than 180 from each other.

Referring now to the drawings, FIGS. l-3 illustrate a ladder 10 comprising a pair of vertical side rails 11 having a plurality of horizontal rungs 13 interconnected therebetween. 1 1

The ladder 10 is adapted to be supported on the ground by leveling means 20 which functions to enable the ladder 10 to be supported in an upright position on any type of sloping terrain.

The leveling means 20 comprises a pair of brackets 21 attached to the bottom ends of the side rails 11 by means of a plurality of bolts 23. The lower portions of the brackets 21 provide a journal bearing for rotatively receiving a torsion bar 25. The torsion bar 25 extends across the bottom of the ladder 10 and beyond the side rails 11. Two legs 27 are connected, one at each end, to the torsion bar 25 and extend radially outward therefrom. As shown in FIGS. 1, 4, and 5, the two legs 27 are oriented 180 apart to extend in opposite radial directions from the torsion bar 25.

Referring to the drawings, FIGS. 1-5, the outer end I of each leg 27 has a pivot pin 29 connected thereto with each pin 29 being parallel to the torsion bar 25. A shoe 30 is pivotally mounted on each pin 29.

A locking means assembly 40 is provided for locking the torsion bar 25 against rotation. The locking assembly 40 comprises a locking wheel 41 fixedly mounted on the one end of the torsion bar 25 adjacent the one leg 27. The locking wheel 41 includes a plurality of teeth 43 mounted about the periphery thereof.

The locking assembly 40 further comprises a locking pawl 45 pivotally mounted on the outside of one of the side rails 11, directly over the locking wheel 41. The locking pawl 45 is pivotally connected to the side rail 11 by means of a pin 47 which is affixed to the respective bracket 21. The lower end of the locking pawl 45 includes a protuberance 49 which is adapted to engage the teeth 43 of the locking wheel 41. The upper end of the locking pawl 45 forms a handle 51 which extends up the side of the side rail 11 to be hand manipulated. A spring 53 is attached at one end to a bolt 23 and at the other end to the handle 51 for applying a bias on the locking pawl 45 to force the protuberance 49 into engagement with the teeth 43 of the locking wheel 41.

Finally, a safety pin 55 extends through the side rail 11, with the outside end thereof forming a stop to prevent the locking pawl 45 from becoming disengaged from the locking wheel 41.

In setting up the ladder 10, the safety pin 55 is removed from the side rail 11 to enable the locking pawl 45 to pivot and be hand-manipulable.

The two side rails' 11 of the ladder 10 are then grasped with both hands and the ladder is movable in the'conventional manner. If desired, the locking pawl 45 can be simultaneously grasped with the one hand to be hand manipulated while the operator can still use two hands to support the ladder. The locking pawl handle 51 extends upwardly a sufficient distance to enable the operator to grasp the side rail 11 at a point where he can easily maneuver the ladder 10.

The ladder 10 is then positioned against a wall with the bottom end being positioned approximately one fourth of its extended length away from the wall. In order to set the ladder down on the sloping terrain, the handle 51 of the locking pawl 45 is hand moved against the bias of the spring 53 to disengage the locking pawl from the locking wheel 41. This action enables the torsion bar 25 to rotate freely.

Then, upon setting the ladder 10 down, the shoe 30 on the high side of the slope is the first to contact the ground (assuming the shoes 30 are at the same initial height). Thereafter, further lowering of the ladder causes the first shoe 30 to act as a fulcrum to enable-the leg 27 on that side to rotate the torsion bar 25. This movement causes the first shoe 30 and leg 27 to rotate upwardly with respect to the torsion bar 25 while the other shoe 30 and leg 27 is caused to rotate downwardly with respect to the torsion bar 25. This angular movement continues until both shoes are firmly planted on the ground. At this point, before looking the torsion bar, the ladder may be pre-loaded to sink the shoes to equalized pressure if the supporting surface is soft or unequally firm. It is important to note that during the above adjustments the ladder is in an upright position, perpendicular to the horizon, resting on a firm, level base (the torsion bar 25), regardless of the characteristic or condition of the supporting terrain.

With both shoes 30 firmly placed, and the ladder 10 in an upright position, the locking pawl handle 51 is released to enable the locking pawl 45 to be biased into engagement with the locking wheel 41. This locks the torsion bar 25 and the legs 27 against further rotation, to keep the torsion bar 25 in the leveled position. The safety pin 55 is then reinserted within the side rail 11 to prevent the locking pawl 45 from being-accidently moved out of engagement with the locking wheel 41.

The ladder is now in condition for the operator to climb.

If it is desired to move the ladder 10 to a new position where the condition of the terrain is different, the entire procedure described above is repeated to enable the torsion bar to be rotated to a new position. Two different operating positions are shown in FIGS. 4 and 5.

FIG. 6 shows a second embodiment of the locking assembly, generally indicated by arrow 60, which is adapted to lockingly engage the teeth 61 of a locking sector 63. The locking sector 63 is fixedly mounted on one end of the torsion bar 25. A stop 64 limits the angular travel of the locking sector 63. As in the first embodiment, two legs 27 are connected, one at each end, to the torsion bar 25. Each leg 27 is connected to a pivot pin 29 which, in turn, pivotally supports a shoe The locking assembly further includes a pawl assembly 65 which is comprised of a locking pawl 66 and a handle 67, the two being interconnected by a fastener 68. The locking pawl 66 and the handle 67 are both pivotally connected by a pin 69 to the end plate 70 of the ladder side rail 71. Therefore, the pawl assembly 65 is pivotable about pin 69 as a unit. A spring 73 is connected to one end of the pawl assembly 65 by an elongated pin 75, and to the end plate 70 by an elongated pin 76. The spring 73 is positioned on the pins 75 and 76 at a fixed distance from the end plate 70 to provide clearance for the spring 73 when it passes over-center of the pin 69; inupwardly direction during locking of the locking assembly 60, downwardly during unlocking. Also shown is a manually insertable, and removable, safety pin 77. When the pawl assembly 65 is engaged with the teeth 61 of the locking sector 63, the spring 73 will maintain this locked engagement. The safety pin 77 is inserted to ensure against inadvertant unlocking. Finally shown is a guard 78 which protects the locking assembly 60; the guard 78 also acts as a stop for a downward slidable upper ladder extension, if utilized.

The pawl assembly 65 is shown in its locked position with respect to the locking sector 63. To unlock, the safety pin 77 is removed and the lower end of the handle 67 of the pawl assembly 65 is pivoted upwardly in a clockwise direction. This movement can be easily accomplished with the foot of the operator. Once the centerline of the spring 73, formed between the pins 75 and 76, is below the center of the pin 69, the spring 73, unaided, will snap the pawl assembly 65 to a rested, unlocked position against the pin 76. The spring 73 will maintain the pawl assembly 65 in the unlocked position until the operator moves the pawl assembly 65 counterclockwise against initial tension in the spring 73. Once the centerline of the spring 73 is above the center of the pin 69, the spring 73 will snap the pawl assembly 65 toward the teeth 61 of the locking sector 63. After the pawl assembly 65 is engaged in the locked position, the safety pin 77 is inserted. In the locked position, the ladder is now ready for use. It is to be noted that, prior to locking, the normal setting up of the ladder would include preloading if the soil were unevenly firm, the process being detailed in the description of the first embodiment.

FIG. 7 shows a third embodiment of the locking assembly, generally indicated by arrow 80. In this embodiment each end of the torsion bar 25 is connected to a leg 27 which, in turn, is connected via a pin 29 to a shoe 30. The one unshown leg 27 is shaped to accommodate the attachment of the torsion bar 25 and the pin 29. The leg 27 shown in FIG. 7 is shaped to also accept a pin 81 which pivotally forms the connection between the leg 27, shown, and the one end of a locking arm 82. The other end of the locking arm 82 is adapted to ride along the edge 83 of the support plate 84 of the side rail 85. This is accomplished by a U-shaped fitting 86, extending over and around the edge 83, the fitting 86 being attached to the locking end of the locking arm 82. The inner surfaces of the U-shaped fitting 86 surround both sides of the support plate 84; and a roller 87 contained within the fitting 86 slidably engages the edge 83 of the support plate 84. A spring 88 is provided to maintain this engagement. The locking arm 82 further includes a movable pin 89 housed in the fitting 86. The pin 89 is adapted to extend through any one of a plurality of holes 90 formed on the support plate 84, and on through a hole formed in the other leg of the U- shaped fitting 86. The plurality of holes 90 provides the locking arm 82 with a plurality of angular positions or settings in order to enable the locking arm 82 to fix the angular position of the leg 27. A stop 91 limits the angular travel of the leg 27. To operate this embodiment of the present invention, the movable pin 89 is turned to unlock, pulled into the housing of fitting 86, and again turned to hold the pin 89 disengaged. This permits the roller 87 of the locking arm 82 to freely slide along the edge 83 of the support plate 84. The unlocked torsion bar 25 is free to rotate to allow the legs 27 to pivot until the shoes 30 are firmly planted on the ground. The pivoting of the legs 27 causes the locking arm 82, shown in lowest position, to move up or down along the edge 83 while pivoting about the pin 81 in the process. After the locking arm 82 stops, the movable pin 89 is turned to permit insertion from its disengaged position; the pin 89 is then pushed to fit through the registering hole 90 located in line with the pin 89 at that angular position of the locking arm 82. The pin 89 is pushed through the hole 90 and through the matching hole of the second leg of the U-shaped fitting 86. The pin 89, now engaged to carry locking loads in double shear, is turned by its handle and locked against withdrawal. In the locked position, the ladder is now ready for use. It is to be noted that, prior to locking, the normal setting up of the ladder would include preloading if the soil were unevenly firm, the process being detailed in the Description of the First Embodiment.

FIG. 8 shows that the shoes of the apparatus are beveled or curved on the bottom surface thereof to more readily accommodate sloping terrain.

FIG. 9 shows a leg connected to each end of the torsion bar, the legs extending radially outward therefrom but not fixed at from each other.

As can be seen, leveling means are provided to maintain the ladder in upright position with four-point support, in all types of sloping terrain on soft or unequally firm soil. In actual operation, the user will readily perceive the inherent self-seeking leveling feature of the torsion bar and shoes in soft terrain during ladder preloading prior to locking the torsion bar.

It should be noted that various modifications can be made to the apparatus while still remaining within the purview of the following claims As examples: (1) the locking assemblies shown in FIGS. 1, 6, and 7 can be re-arranged to function when mounted on either one of the pair of side rails, and on either the inside or the outside of either of the side rails; (2) the two end plates can be formed with angular extensions that are offset toward the center of the ladder in order to house the torsion bar, the legs, the shoes, and the locking assembly under the ladder and within the space between the side rails; (3) the torsion bar can be comprised of more than one element to provide an adjustment in the length of the torsion bar to fit various width ladders; (4) each of the legs can be comprised of more than one element to provide adjustable length legs; (5) the torsion bar or portion thereof and one leg can be a shaped single element; (6) a full-length torsion bar and both legs and both pivot pins, or any combination thereof, can be a shaped single element; (7) in FIG. 7, the slidable engagement between the edge of the support plate and the roller of the locking arm can be accomplished by providing a guiding flange along the edge of the support plate (instead of on the end of the locking arm), and changing the spring to compression-type. These and various other possible modifications are normal considerations during the production development of the present invention, all remaining within the purview of the following claims.

What is claimed is:

1. An adjustable support apparatus for a portable ladder, said ladder having two side rails joined at regular intervals by interconnecting crosspieces, said support apparatus comprising:

an elongated torsion bar rotatively journaled adjacent the bottom ends of said side rails, said torsion bar being positioned parallel to said interconnecting crosspieces;

a leg on each end of said torsion bar, said legs extending radially outward from said torsion bar substantially 180 from each other;

a shoe pivotally mounted on the outer end of each leg, each shoe having a surface adapted to be supported on the ground; and

means for locking said torsion bar against rotation after said legs have assumed their desired position with respect to the ground.

2. The invention of claim 1 wherein said torsion bar comprises an elongated hollow cylindricaltube.

3. The invention of claim 1 wherein said torsion bar is journaled on a pair of brackets mounted on the side rails of the ladder.

4. The invention of claim 1 wherein said shoes are pivotally connected to pivot pins which in turn are attached to said respective legs.

5. The invention of claim 1 wherein said locking means comprises a locking wheel with peripheral teeth,

said wheel being coaxial with, and fixedly mounted on, said torsion bar.

6. The invention of claim 1 wherein said locking means comprises a locking wheel sector with peripheral teeth, said wheel sector being coaxial with, and fixedly mounted on, said torsion bar. 7. The invention of claim 5 wherein said locking means further comprises a locking pawl pivotally mounted on siad ladder, said locking pawl having one end adapted to be pivoted in one position to engage the locking teeth of said locking wheel.

8. The invention of claim 6 wherein said locking means further comprises a locking pawl pivotally mounted on said ladder, said locking p'awl having one end adapted to be pivoted in one position to engage the locking teeth of said locking wheel sector.

9. The invention of claim 7 wherein said locking means further comprises means for securing said locking pawl in said one position, engaged between two teeth to resist load in either direction, clockwise or counterclockwise.

10. The invention of claim 7 wherein said locking pawl is pivotally mounted on one of the side rails of the ladder.

11. The invention of claim 8 wherein said locking pawl is pivotally mounted on one of the side rails of the ladder.

12. The invention of claim 10 wherein said locking wheel is mounted on said torsion bar adjacent one of said side rails, on the same side of said side rail as said locking pawl.

- 13. The invention of claim 11 wherein said locking wheel sector is mounted on said torsion bar adjacent one of said side rails, on the same side of said side rail as said locking pawl.

14. The invention of claim 1 wherein said locking means comprises a locking arm pivotally attached at one end to one of said legs at a location different than where said respective shoe is attached.

15. The invention of claim 14 further including means for fixing the other end of said locking arm in order to lock the angular position of said leg.

16. The invention of claim 15 wherein said fixing means further includes a plurality of holes formed on said side rail and a pin movably mounted on said locking arm for extending into any one of said holes to fix the angular setting of said locking pawl.

17. The invention of claim 16 wherein said pin is separately stored for use and not movably mounted on said locking arm.

18. The invention of claim 1 wherein said legs extend radially outward from said torsion bar with said legs being radially oriented other than from each other. 

1. An adjustable support apparatus for a portable ladder, said ladder having two side rails joined at regular intervals by interconnecting crosspieces, said support apparatus comprising: an elongated torsion bar rotatively journaled adjacent the bottom ends of said side rails, said torsion bar being positioned parallel to said interconnecting crosspieces; a leg on each end of said torsion bar, said legs extending radially outward from said torsion bar substantially 180* from each other; a sHoe pivotally mounted on the outer end of each leg, each shoe having a surface adapted to be supported on the ground; and means for locking said torsion bar against rotation after said legs have assumed their desired position with respect to the ground.
 2. The invention of claim 1 wherein said torsion bar comprises an elongated hollow cylindrical tube.
 3. The invention of claim 1 wherein said torsion bar is journaled on a pair of brackets mounted on the side rails of the ladder.
 4. The invention of claim 1 wherein said shoes are pivotally connected to pivot pins which in turn are attached to said respective legs.
 5. The invention of claim 1 wherein said locking means comprises a locking wheel with peripheral teeth, said wheel being coaxial with, and fixedly mounted on, said torsion bar.
 6. The invention of claim 1 wherein said locking means comprises a locking wheel sector with peripheral teeth, said wheel sector being coaxial with, and fixedly mounted on, said torsion bar.
 7. The invention of claim 5 wherein said locking means further comprises a locking pawl pivotally mounted on siad ladder, said locking pawl having one end adapted to be pivoted in one position to engage the locking teeth of said locking wheel.
 8. The invention of claim 6 wherein said locking means further comprises a locking pawl pivotally mounted on said ladder, said locking pawl having one end adapted to be pivoted in one position to engage the locking teeth of said locking wheel sector.
 9. The invention of claim 7 wherein said locking means further comprises means for securing said locking pawl in said one position, engaged between two teeth to resist load in either direction, clockwise or counterclockwise.
 10. The invention of claim 7 wherein said locking pawl is pivotally mounted on one of the side rails of the ladder.
 11. The invention of claim 8 wherein said locking pawl is pivotally mounted on one of the side rails of the ladder.
 12. The invention of claim 10 wherein said locking wheel is mounted on said torsion bar adjacent one of said side rails, on the same side of said side rail as said locking pawl.
 13. The invention of claim 11 wherein said locking wheel sector is mounted on said torsion bar adjacent one of said side rails, on the same side of said side rail as said locking pawl.
 14. The invention of claim 1 wherein said locking means comprises a locking arm pivotally attached at one end to one of said legs at a location different than where said respective shoe is attached.
 15. The invention of claim 14 further including means for fixing the other end of said locking arm in order to lock the angular position of said leg.
 16. The invention of claim 15 wherein said fixing means further includes a plurality of holes formed on said side rail and a pin movably mounted on said locking arm for extending into any one of said holes to fix the angular setting of said locking pawl.
 17. The invention of claim 16 wherein said pin is separately stored for use and not movably mounted on said locking arm.
 18. The invention of claim 1 wherein said legs extend radially outward from said torsion bar with said legs being radially oriented other than 180* from each other. 